Steel for high temperature cementation



Nov. 3, 1964 Filed Jan. 4, 1962 CEMENTATION DEPTH, mm

5 Sheets-Sheet 1 CEMENTATION TIME,HR.

INVENTOR HAJIME NAKAMURA ATTORNEY Nov. 3, 1964 HAJIME NAKAMURA 3,155,549

STEEL FOR HIGH TEMPERATURE CEMENTATION Filed Jan. 4, 1962 5 Sheets-Sheet 2 Nov. 3, 1964 Filed Jan. 4, 1962 ETMIA ){ICKERS HARDNESS. Hv

HAJIME NAKAMURA 3,155,549-

STEEL FOR HIGH TEMPERATURE CEMENTATION 5 Sheets-Sheet 3 TEMPERATURE, C

Carbon steel A for high tempicementmion in case of 900 which is given solid curburizoiion util30Cfor8hours Alloy-steel Ffor high temp. oememuiion in case of which 800 ,r\ is given solid curburizciion o1 00C for8hours Commercial curbon-s1eel S|5CK foreementufloninoase 700 of which isgiven solidoubu'lzuiion ot950Cfor8hours 100 I i J i DEPTH FROM THE CEMENTATION SURFACE,mm

INVENTOR HAJIME NAKAMURA ATTORNEY Nov. 3, 1964 HAJIME NAKAMURA STEEL FOR HIGH TEMPERATURE CEMENTATION Filed Jan. 4, 1962 Carbon steel f. high-temp.

cementation (A) 11000 x 8 hrs cementation fiypo-eutectoid-part austenite crystal grain: AS'I'M grain size Ho. 8

Carbon steel 1. high-temp.

FIG. IO

cementation (A) 1100C x 8 hrs. cenentation Central-part ferrite crystal ins rain size no. 8

5 Sheets-Sheet 4 Commercial carbon steel 1:.

cementation (8150K) 1100C x 8 hrs cementation flypo-eutectoid-part auatenite crystal grains ASEM grain size lb. 1

FIG. ll

Conner-c111 caron steel 2. comentation (3150K) 11006 x 8 hrs cementation Central-part ferrite crystal grain: ASTM grain size No. 3.5

INVENNR.

HAJIME NAKAMIRA Attorneys 1964 HAJIME NAKAMURA 3,

STEEL FOR HIGH TEMPERATURE CEMENTATION Filed Jan. 4, 1962 7 5 Sheets-Sheet 5 FIG. l3

211 00 xhOO Alloy steel f. hi h-temp. Commercial alloy steel 1. cementation (8% cementation (SOP-1) 1100C x 8 hrs cementation 1100C x 8 hrs cementation Hyper-eutectoid-part austenite Hy er-eutectoid-part auatenite crystal grains crystal grains ASTM grain size No. 9 ASTM gr ain size No. 1

INVENTOR.

HAJIHE NAKAMURA Attorneys United States Patent 3,155 549 STEEL FOR HIGH TEMPERATURE CEMENTATION Hajime Nakamnra, Tokyo-to, Japan, assignor to Ishrkawajima-Harima Jukogyo Kabushiki Kaisha, Tokyo-to, Japan, a company of Japan Filed Jan. 4, 1962, Ser. No. 164,290 Claims priority, application Japan, Mar. 11, E961, 36/ 8,485 4 Claims. (Cl. 148-39) The present invention relates to a steel for high temperature cementation.

Though there is a tendency that the required conditions of material become more strict and deeper cementation is being sought with the recent improvement of performance and durability 'of the machine elements in the field of mechanical engineering, by the standard process of cementation of the present day which cements under 950 C. of cementation temperature it takes such long hours and needs so great an increase of the amount of work and invites so great a delay of work in 'order to get a deeper cementation that it is considered to be quite impossible to get the necessary deeper cementation by the present technique of cementation.

As the certain depth of cementation can be got by selecting the time and temperature properly when the same process of cementation is given to the same material, the time of cementation may be short, if the temperature of cementation is high. For example, to get the same cementation depth as that which is obtained by 8 hours cementation at 925 'C,, it takes only 1.5 hours, if the cementation is given at ll00 C. But when the cementation is given at such high temperature, in case of present case hardening steel the crystal grains become so coarse that it becomes remarkably brittle, and therefore the cementation at such high temperature has been infeasible.

As is seen in FIGURE 1, however, it is evident how the cementation at high temperature is profitable, and as the longer the cementation time become the more saturated tends to be the depth of cementation, there is no adequate Way other than the cementation at high temperature in order to get deeper cementation. Therefore, if the case hardening steel can be got that yields no coarse crystal grains and yields no other defects when the cementation is given to it at high temperature, many problems that have not been solved yet could be solved by a single efiort.

This invention was predicated on the discovery that a steel with a structure containing precipitated aluminum ice nitride is effective to prevent the growth of the austenite grains during cementation at a high temperature, after many experiments that had been done on various case hardening steels in quest of one that yields no growth of crystal grains and no other defects at the time of cementation at high temperature; and this invention relates to the steel for high temperature cementation, the composition of which includes 0.05-0.25% carbon, 0.15-0.40% silicon, less than 1.00% manganese, and may contain, beside these, one or more of 1-4.5% nickel, 0.42.5% chrome, 0.l0-1.0% molybdenum, and contains more than 0.04% precipitated aluminum nitride and ODS-0.001% dissolved metallic aluminum.

The accompanying drawings explain and illustrate the inventive steel for high temperature cementation.

FIGURE 1 shows the relation between the depth, the temperature and the time of cementation for case-hardening steel by a solid carburizer. FIGURE 2 shows the relations between precipitated aluminum nitride contained in the steel and the austenite grain size when the standard cementation (925 C. 8 hours) and the high temperature cementation (1l00 C. 8 hours) are given to various case hardening steel. FIGURE 3 shows the relation between the ferrite grain size and the precipitated aluminum nitride when the same cementation processes are given as in the case shown in FIGURE 2. FIGURE 4 shows the solubility curve of the aluminum nitride contained in the case hardening steel. FIGURE 5 shows the change of the austenite grain size when high temperature cementation steel of this invention and the commercial steels for cementation are cemented for 8 hours at various temperatures of cementation. FIGURE 6 shows the change of the ferrite grain size due to the same cementation processes as in FIGURE 5. FIGURE 7 shows the distribution of hardness in the high temperature cementation steels of this invention and in the commercial cementation steel at the end of 8 hours cementation at various temperatures, followed by the primary quenching from 930 C., the secondary quenching from 800 C., and tempering at 180 C. in that order. FIGURES 8 to 13 are microphotographs that show the different degrees of growth of the austenite grains and the ferrite grains that are seen when the high temperature cementation steels of this invention and the commercial cementation steels are cemented at high temperature.

In Table 1 are shown the chemical compositions of some of the steels for cementation that were used in the experiments in the course of this invention.

S15CK, SCM21, SNC22, SNCM23 in the table represent the steels for cementation that are currently popular.

Table 1.Chemical Compositions of Various Steels for Cementation T esled (Percent) Material Mark C Si Mn P S N 1 Cr M0 Cu Carbon steel for high temperature cementation- A 0.15 0.25 0. 61 Do B 0.07 0.31 0. D0 0 0.09 0.25 0.82 Do D 0.08 0. 21 0.85 Commercial carbon steel for cementation 8150K 0.14 0.33 0. 44 Alloy steel for high temperature cementation- 0. 19 0. 35 0.82 Do A 0.12 0.32 0. 59 Do 0.14 0.33 0.64 Commercial alloy steel for cementation SCM 0.15 0. 21 0.68 Do 0.16 0.81 0.55 Do SNCM23..- 0.18 0.26 0.67

Table 1.Clzemieal Compositions of Various Steels for Cemeizmtiolr Tested (Percent)-Cntinucd Total oi Material Marl: Total N AlN A1 0 Metal- Ti. Zr. Be. nitrides, Remarks Al lie Al except AlN Carbon steel for high temperature A 0.104 0.036 0.096 0.009

cementation.

D0 B 0.006 0.017 0.0025 0.007 0.001 Be. 0.12 0.022 Do 0-- 0. 00 0.021 0.016 0. 008 TitisAadded 0 D0 D 0.11 0.036 0.056 0.021 Zrtis added 0 1 Cgnltmercialcarhon steel for cemen- $150K 0.031 0.010 0.020 0.008

a H. Alloy steel for high temperature cc- E 0.115 0.037 0.107 0.014

mentation.

o F- 0. 095 0. 034 0. 092 0.011 D0 G 0.100 0.038 0.107 0.011 Clgnmercialalloy steel ior eementa- SCM21. 0.005 0.008 0.003 0.004

Do SNC22 0.028 0.008 0.010 0.008 D0 SNCM23 0.042 0.010 0.025 0.006

l Beryllium nitrides.

1 Titanium nitrides.

3 Zirconium nitrides.

When a standard cementation is given at 925 C. for 8 hours, and a high temperature cementation is given at 1100 C. for 8 hours, to the steel for cementation of various corn-position, the relation between aluminum nitride contained in the said steel and austenite and ferrite grain size is as shown in FIGURE 2 and FIGURE 3, and it is evident that the growth of the crystal grains is prevented when the quantity of aluminum nitride increases to more than a certain amount, even if a high temperature cementation is given. The amount of aluminurn nitride necessary for preventing the growth is much higher as compared with that for the commercial cementation steel which is, at most, less than 0.03%. Namely, the prevention of the grain growth begins when aluminum nitride contained in steel is about 0.04%, and

is stimulated when it is about 005-0.06%, and is complete when it is more than 0.06%. FIGURE 4 shows the solubility curve of aluminum nitride which was obtained by the examination of aluminum nitride contained in steel specimens heated [for 8 hours at each designated temperature. For example, in case of steel that contains 0.09% aluminum nitride, there is almost no decrease of the precipitated aluminum nitride even if it is heated for 8 hours at 1100 C., and when it is heated for 8 hours at 1200 C. it still contains 0.05-0.06% aluminum nitride in precipitation and the growth of the crystal grains is hardly seen.

Table 2 shows the results of the specimens that were noted in Table l subjected to cementation for 8 hours at 925 C. and to a high temperature cementation for 8 hours at 1100 C., as the case may be.

Table 2.-Austenite Grain Size and Amount of AlN Contained When a High Temperature Cementalion Was Given to Various Steels STANDARD CEMENTATION Tcrnpera- Hours of AlN, per ASTM Material Mark ture oi eementacent after grain size eementation, hrs. eementanumber tion, 0. tion Carbon steel for high temperature cementa- 925 8 0. 090 0 tion.

D0 925 8 '0. 025 9 Do 925 8 '0. 081 9 D0 925 8 '0. 084 10 Commercial carbon steel for eementation 925 8 0. 029 8 Alloysteel for high temperature cementation. 925 8 0. 107 0 Do 925 8 0. 092 10 D0 925 8 0.107 9 Commercial alloy-steel for eementatiou M 025 8 0. 003 6 Do SNCZZ 925 8 0,019 7, 5 Do SNCM23.-. 025 8 0.025 9 HIGH TEMPERATURE CEMENTATION Tempera- Hours of AlN, per- ASTM Material Mark ture of eementacent after grain size eementetion, hrs. cementanumber tiun, 0. tion Carbon steel [or high temperature cementa- A 1.100 8 0.081 9 t on.

Do B 1,100 8 '0. 028 5 D0 0 1,100 8 0. 070 8 Do D 1,100 8 '0. 079 10 Commercial carbon steel for cementatloru..- $150K 1, 8 0. 017 1 Alloy-steel for high temperature eementation. E 1, 100 8 0. 100 8 Do F 1,100 8 0.087 0 Do. G 1,100 8 0.102 0 Commercial alloy-steel tor eementation SCM21- 1,100 8 0. 003 1 D0 SNC22 1,100 8 0. 005 1 D0 SNCM23 1,100 8 0.017 2 Mark denotes the total sum of AlN' and other nitrides.

FIGURE and FIGURE 6 show the change of th austenite and ferrite grain size that occurs when several kinds of steel for high temperature cementation due to this invention and commercial steel for cementation are cemented for 8 hours at each designated temperature. In the case of carbon-steel A for high temperature cementation and alloy-steel F for high temperature cementation of this invention the growth of the crystal grains is hardly seen, whereas in the case of commercial steel for cementation SISCK and SNC22 crystal grains begin to become coarse at 1000-1050 C.

The uniform grains and the irregular cementation (sooalled soft spot), which are olten brought about in a high temperature cementation, are due to the solid solution of metallic aluminum contained in steel for cementation, and to prevent this it is necessary to keep the amount of the metallic aluminum dissolved in steel matrix as small as possible. As it was made evident from many experiments that these defects are brought about if more than 0.05 metallic aluminum is contained in solid solution, in this invention the amount of dissolved metallic aluminum is limited to less than 0.05

The present inventor discovered that some other nitrides beside aluminum nitride are also powerful in preventing the growth of the austenite grain size in the case of high temperature cementation steels. And even when a high temperature cementation is given to a steel, to which titanium, zirconium, beryllium etc. are added and in which a part or most of aluminum nitride is displaced by beryllium nitride, titanium nitride and zirconium nitride, the growth of the crystal grains is hardly recognized. For example, C and D in the Table 1 are the steel containing aluminum nitride, which is also made to contain titanium nitride or zirconium nitride by adding titanium or zirconium, and the growth of the crystal grains during the high temperature cementation was stopped completely and very excellent cemented layer without in uniform grains and irregular cementation was obtained. And in the case of steel B that contains 0.022% beryllium nitride, most of its aluminum being displaced by beryllium, the growth of crystal grains is much smaller as compared with one that contains as much aluminum nitride. From these results, it is easily concluded that the addition of boron should also be efiective, as it is the same kind of element as titanium, zirconium and beryllium that compose nitride. When titanium, zirconium, beryllium, boron etc. are added, it is possible as said before to prevent to some extent such detects as in uniform grains and irregular cementation caused by the dissolved metallic aluminum, and, thereforethe amount of dissolved metallic aluminum in steel is allowed up to 0.10%.

FIGURE 7 shows the distribution curve of the hardness through a cross seotion of material, when A and F of the cementation steels due to this invention and S15 CK of commercial cementation steel are cemented using solid carburizer for 8 hours at 1l130 C., 1100 C. and 950 C., respectively. It is to be seen that in any one of high temperature cementation steels of this invention there is very few irregular distribution of hardness, and an excellent layer of cementation is obtained.

And, if FIG. 8 and FIG. 10, that show the hypo-eutectoid-part austenite crystal grains and the central-part ferrite crystal grains of the steel A for high temperature cementation of this invention as subjected to cementation for 8 hours at 1100 C., are compared with FIG. 9 and FIG. 11, that show the hypo-eutectoid-part austenite crystal grains and the central-part ferrite crystal grains of a commercial steel for cementation, S15CK, as cemented under the same condition, and if FIG. 12, that shows the hyper-eutectoidpart austenite of the steel E for high temperature cementation of this invention as cemented for 8 hours at 1100 C., is compared with FIG. 13, that shows hyper-euctectoidpart austenite of a commercial steel for cementation, SCM21, as cemented under the same condition, the growth of the crystal grains in the case of the steels for high temperature cementation of this invention is seen to be less as compared with the case of the commercial steels for cementation.

What I claim is: 1. A case carburized steel having the approximate composition:

005 %-0.25 carbon 0.15%0.40% silicon less than 1% manganese said steel having been carburized at a temperature of above about 925 C. and containing in the carburized state between about 0.04% and about 0.10% precipitated aluminum nitride and from about 0.001% to 0.05% of dissolved metallic aluminum.

2. A case carburized steel having the approximate composition:

0.05%0.25% carbon 0.15%0.40% silicon less than 1% manganese and containing further at least one of the following elements in the approximate amounts indicated:

1.0%-4.5% nickel 0.4%-2.5% chromium 0.10%-1.0% molybdenum said steel having been carburized at a temperature of above about 925 C. and containing in the carburized state between about 0.04% and about 0.10% precipitated aluminum nitride and from about 0.001% to 0.05% of dissolved metallic aluminum.

3. The steel of claim 1 in which a portion of the aluminum nitride is replaced by a member selected from the group consisting of the nitrides of beryllium, titanium, zirconium and boron, and wherein the amount of dissolved metallic aluminum is from 0.001% to 0.10%.

4. The steel of claim 2 in which a portion of the aluminum nitride is replaced by a member selected from the group consisting of the nitrides of beryllium, titanium, zirconium and boron, and wherein the amount of dissolved metallic aluminum is from 0.001% to 0.10%.

References Cited in the file of this patent UNITED STATES PATENTS 2,528,867 Day Nov. 7, 1950 2,797,162 Korcynsky June 25, 1957 FOREIGN PATENTS 786,993 Great Britain Nov. 27, 1957 808,556 Great Britain Feb. 4, 1949 

0.05%-0.25% CARBON 0.15%-0.40% SILICON LESS THAN 1% MANGANESE
 1. A CASE CARBURIZED STEEL HAVING THE APPROXIMATE COMPOSITION: 